The human cochlea or inner ear has been inaccessible to high-resolution imaging and visually guided surgical manipulation, due to its complex structure, small size, fragility, and embedded location deep within the temporal bone. This inaccessibility to microscopic inspection has long been a major hindrance to advances in clinical otology. Yet historically, the ability to acquire high-resolution images within the body has resulted in numerous biomedical breakthroughs. For visualizing the cochlea, the emerging microscopy technology known as 'microendoscopy'offers the possibility of minimally invasive imaging at resolution sufficient to visualize microanatomy and even cellular details. Thus, this R21 application proposes the development of a high-resolution microendoscope suitable for imaging the human inner ear. An accompanying surgical positioning apparatus compatible with both our micro- optical instrument and human temporal bone structure will also be developed. Although no live human work is planned during the two-period of this grant, all validation efforts in animal models and human cadaver temporal bones will be performed with the long-term goal of beginning clinical testing under a follow-up grant application. The specific aims of this project are: Aim 1: Design, build, and test a microendoscope to image human cochlear microanatomy and microvasculature. This will involve a novel 500-micron-diameter endoscope probe that can perform both bright-field and fluorescence imaging, as well as novel kinematic joints based on magnetic force and air bearings. Once the system is designed and built, the mechanics of endoscope manipulation will be tested using plastic temporal bone models and human cadaver temporal bones. Aim 2: Test the ability of fluorescence microendoscopy to provide non-destructive, high-resolution imaging of cochlear blood flow and microanatomy in the cochleae of living guinea pigs. To assess the effects of microendoscopy on auditory function and cochlear microarchitecture, hearing measurements will be performed at multiple experimental time points and compared to post hoc histological analyses of the cochlea. The ability to image blood flow and microanatomy within the human cochlea would be a tremendous boon both for clinicians seeking surgical guidance during cochlear implantation or other otologic procedures, as well as for basic researchers seeking to correlate cellular characteristics of the living cochlea with physiological measures of hearing. Thus, if our work is successful it should have significant impact on both clinical otology and basic hearing research. PUBLIC HEALTH RELEVANCE: Project Narrative Medical breakthroughs have often followed the development of new techniques for visualizing the human body, but the inner ear or cochlea remains one of the body's last areas that has resisted high-resolution imaging in living subjects. Using an innovative form of miniaturized microscopy known as microendoscopy, the proposed research concerns the design, construction, and validation of novel instrumentation for minimally invasive imaging of the human inner ear. This new technology will allow inner ear surgeons to visualize the inside of the cochlea for the first time during surgery, which could lead to major breakthroughs in our understanding of and treatments for human deafness.